There is a general interest in the manufacture and use of optical sensors (SERS-sensors) with nanostructured metal surface. FIG. 13A illustrates one type of conventional SERS-sensor with nanostructured metal coverage. This SERS-sensor includes a substrate 132 of copper or silicon oxide, a dense hexagonal array of nanospheres 131 of polystyrene or silicon oxide arranged on the substrate surface, and a metal film 29a over the array of nanospheres (U.S. Patent Application Publication No. 2009/0118605, incorporated herein by reference). The diameter of the nanospheres is 390 nm and the thickness of metal film of silver is 200 nm. This reference also discloses examples of conventional SERS-sensors with a hexagonal array of metal triangles on the surface of the substrate. These sensors can be manufactured by nanosphere lithography (NSL) in which a monolayer of nanospheres is deposited on a substrate surface with dense hexagonal packing, metal is then deposited through the nanospheres, and then the nanospheres are removed. Disadvantages of the NSL method can include low throughput and difficulties in forming large area substrates. Disadvantages of conventional SERS-sensors can include a low surface density of the nanospheres and metal triangles in the arrays and small array sizes which may not surpass a few millimeters.
One type of conventional optical sensor is disclosed in U.S. Pat. No. 7,453,565, incorporated herein by reference. This SERS-sensor is illustrated in FIG. 13B and has a substrate 133 of aluminum, a template of nanopores in anodic aluminum oxide (AAO) 134, and silver nanoparticles 29 deposited in the nanopores of the AAO template. Between the nanoparticles 29 there are the gaps 14. Disadvantages of methods of manufacturing SERS-sensors based on AAO templates can include low throughput, difficulties in forming AAO templates of large area, and instability of the process of forming AAO templates induced by small deviations of critical parameters. A disadvantage of the conventional SERS-sensor can include a small size of the AAO template which may not surpass a few centimeters.